Vacuum pumps may be fitted to road vehicles with gasoline or diesel engines. Typically, the vacuum pump is driven by a cam shaft of the engine. Therefore, in most vehicles the vacuum pump is mounted to an upper region of the engine. But also configurations where the vacuum pump is mounted to a lower region of the engine are known. In general, two different construction types of vacuum pumps are known, one is the type incorporating a movable piston, and the other is the vane pump. Nowadays, in particular vane pumps are broadly established.
A vane pump of the aforementioned type typically comprises a housing having an inlet and an outlet and defining a chamber within the housing. Moreover it comprises a rotor for rotational movement about a rotational axis within the chamber. This rotor usually is offset with respect to a central axis of the housing, and typically mounted adjacent, or contacting, an inner circumferential wall of the chamber. The rotor drives at least one vane to draw fluid through the inlet into the chamber and out of the chamber through the outlet, so as to induce a reduction in pressure at the inlet. The inlet is connectable to a consumer such as a brake booster or the like. The outlet normally is connected to the engines crankcase, thus the exhaust air is consumed by the engine, via the P.C.V system.
Known in the art are so-called mono-vane pumps or single vane pumps, comprising one single vane, which extends in a radial direction through the whole rotor, so as to project outward on both sides of the rotor and to contact with both vane tips the inner circumferential wall of the chamber. Mono-vane pumps having a rigid vane in general have the drawback that the freedom in designing the profile of the chamber, which is defined by the inner circumferential wall of the chamber, is limited. The profile needs to be formed according to a conchoid of a circle, such that the vane is able to rotate while still contacting with both vane tips the inner wall and to seal against the inner wall accordingly.
To meet such a drawback it has been proposed in DE 40 19 854 to use a single vane which is split in radial direction by a double L-shaped cut. Each tip of the single vane can move independently on the other tip to a certain extent and the profile of a chamber can be designed with a higher degree of freedom. However, a drawback of such a design is the sealing of both parts of the vane against each other as well as the design of the vane tip which is dependent on the split vane arrangement.
Moreover, also multi-vane pumps are known having a plurality of vanes which are provided in a radial or non-radial manner in the rotor and movable independent from each other. With such a multi-vane pump the inner circumferential wall and thus the chamber profile can be designed with a great degree of freedom.
DE 300 46 76 discloses an engine, comprising a chamber and a rotor within the chamber, as well as two movable vanes. The rotor is centrally provided within the chamber so as to form a rotary engine. Each vane can move with its whole length into the respective recess in the rotor and is provided with a spring, so that the vane is biased into an extended position. This design has the drawback that the rotor needs to be large to form two sealing points so as to divide the chamber into sub-chambers and to provide sufficient space, so that the vanes can dive with their whole length into the rotor body. This leads to certain restrictions.